The present invention relates generally to scanning, transmission, and scanning transmission electron microscopes, confocal and scanning confocal (optical) microscopes as well as to x-ray microscopy instrumentation capable of producing images of objects at varying resolutions ranging from the macroscopic to nanometer regime. More particularly, the present invention relates to an electron optical device or a scanning confocal microscope and methods for imaging specimens, such as, high resolution imaging of thick non-optically transparent specimens including imaging of structures buried in thick non-optically transparent specimens.
A wide range of instruments, such as scanning, transmission, and scanning transmission electron microscopes, confocal and scanning confocal optical microscopes as well as to x-ray microscopy instrumentation, can be used today for microscopic studies of materials. Generally confocal and scanning confocal optical microscopy (COM/SCOM) employ visible light as their illumination source to produce a representative image of the specimen, while the electron and x-ray microscopes correspondingly utilize electrons and x-rays as sources. Each of scanning, transmission, and scanning transmission electron microscopes, confocal and scanning confocal optical microscopes as well as to x-ray microscopy instrumentation is capable of producing images of objects at varying resolutions ranging from the macroscopic (mm) through micrometer (xcexcm) to nanometer (nm) regime.
Confocal optical microscopy (COM), due to its dependence upon visible light is limited to applications where researchers study only the surface of optically dense objects, or the internal structure of optically transparent objects which permit light to be reflect or be transmitted from and/or through subsurface features. In Scanning Confocal Optical Microscope (SCOM), images are obtained using a confocal technique, where the imaging source, sample and detector all lie in conjugate planes, thus reducing the extraneous light scattering from blurring the image. However, the use of light precludes the use of non-transparent specimens that make up the most of the physical science specimens. The COM and Scanning Confocal Optical Microscope (SCOM) typically operates at resolutions of xcx9c500 nm. Of these two modes, the latter transparent mode is the most prolific application particularly in the area of life sciences where the SCOM has made a major impact upon that community.
The scanning electron microscope (SEM) has also gained widespread acceptance as a high resolution (xcx9c10 nm) device for studies of the surfaces of materials of all descriptions in both the life and physical science area, owing to the fact that its imaging signal is principally generated and localized to the near surface zone. The transmission and scanning transmission electron microscope (TEM/STEM) is most often the instrument of choice for studying the internal structure of materials at moderate to very high resolution (xcx9c0.1 nm); however, with the caveat that the specimen of interest must be rendered extremely thin or  less than 100 nm. Finally, the modern x-ray and scanning transmission x-ray microscope (XTM/STXM) utilizes a focused x-ray beam to penetrate thick sections of materials  greater than 5 xcexcm to study, in projection, a materials"" internal structure. Generally these x-ray instruments are located at synchrotron radiation sources and used for studying the internal structure of relatively thick materials, which are not amenable to study by any of the former devices. Currently these x-ray microscopes operate at moderate resolutions of xcx9c200 nm. The cost of synchrotron radiation sources, such as the national synchrotron-radiation light source at Argonne National Laboratory, are generally in the range of hundreds of millions of dollars.
In today""s technologically driven society, a greater and greater number of important devices are being constructed on an ever decreasing size scale. At the same time they are also being fabricated as multi-layered structures to maximize density and minimize size. The most well known example of this construct is the semiconductor microprocessor that can have from one to more than 5 layers within a total thickness on the order of 5-10 microns. Within the individual layers important features can vary in size from 100 xcexcm to the 10 nm level. The role of microscopy when applied to these devices is to characterize the structure of such objects, particularly in scenario where there is some material failure particularly in the sub-micrometer to nanometer scale.
In order to study the detailed internal structure of buried features in optically dense materials from either a fundamental or failure analysis standpoint, researchers today must painstakingly prepare cross-sectional, or plan-view samples of appropriate thickness for use in either the TEM/STEM or the XTM/STXM, since neither the COM/SCOM nor the SEM allow the inspection of internal (buried) layers and/or components. While both TEM/STEM and XTM/STXM allow a modicum of observation to be facilitated, both these generic types of instruments have their respective limitations. While the resolution of the TEM/STEM is orders of magnitude better than the XTM/STXM, this is only true for extremely thin samples. In the TEM/STEM images are mainly produced by measuring the elastically scattered electrons transmitted through the sample, and hence are ultimately limited by this process. To utilize the TEM/STEM researchers must prepare thin sections ( less than 100 nm thick) of a material, and as a result sacrificing adjacent structures in the process. Sample preparation is thus a destructive procedure in the TEM/STEM instrumentation and limits the type of observations that can be conducted. In contrast, the XTM/STXM, is less affected by the scattering process of the primary illumination source, utilizes elastic and inelastic scattering to produce image, and typically employs sample that are tens of micrometers thick. XTM/STXM, however, suffers from reduced resolution when compared to thin film TEM work, long acquisition times, limited fields of view and more importantly, operationally complex procedures which are slow and resource consuming, requiring expensive and frequently large physical facilities such as synchrotron based x-ray sources.
A principal object of the present invention is to provide a scanning confocal microscope and methods for imaging specimens, such as, high resolution imaging of thick non-transparent specimens including imaging of structures buried in thick non-transparent specimens.
Another object of the present invention is to provide an improved method for implementing the imaging of buried or subsurface features of the structure of technologically complex objects such as semiconductor devices at high resolution.
Another object of the present invention is to provide improved methods for implementing a scanning confocal electron microscope (SCEM).
Another object of the present invention is to provide a scanning confocal microscope and methods for imaging specimens, such as, high resolution imaging of thick non-transparent specimens including imaging of structures buried in thick non-transparent specimens substantially without negative effect and that overcome some disadvantages of prior art arrangements.
In brief, a scanning confocal microscope and methods are provided for configuring scanning confocal microscopes for imaging specimens, such as, high resolution imaging of thick nontransparent specimens including imaging of buried or subsurface features of thick nontransparent structures. Novel methods are provided for configuring a scanning confocal microscope, such as a scanning confocal electron microscope (SCEM), to image structures buried in thick specimens, such as specimens greater than five microns (micrometers) thick, utilizing confocal imaging principles.
A scanning confocal microscope includes an illumination source, a specimen, and a detector. The illumination source provides a focused radiation beam that is applied to the specimen. The detector detects an interaction signal from the specimen. The scanning confocal microscope is configured to operate in the confocal imaging mode, where the imaging source, specimen and detector are arranged to be located at conjugate image points by means of lenses while scanning is accomplished by means of an illumination deflection system.
In accordance with features of the invention, the focused radiation beam provided by the illumination source includes an electron beam, a proton beam, an ion beam, or an x-ray beam. The focused radiation beam provided by the illumination source is capable of penetrating thick non-optically transparent specimens, unlike visible light or optical probes that cannot penetrate significant depths in optically dense specimens. The incident probe is sequentially scanned across the region of interest of the specimen and the net integrated confocal intensity at each point is detected and used to provide an image display.